LOW-VOLTAGE OSCILLATOR WITH CAPACITOR-RATIO SELECTABLE DUTY CYCLE AND SINGLE-INPUT SUB-THRESHOLD-CONDUCTING COMPARATORS TO S-R LATCH

摘要

An oscillator operates at a very low voltage yet has a duty cycle that is set by a ratio of capacitors (34,44) that are charged and discharged. Sub-threshold p-channel transistors (80,82) conduct sub-threshold currents below the normal threshold voltage, and drive set and reset inputs of a set-reset S-R latch (40). The S-R latch (40) drives the oscillator outputs. The oscillator outputs feed back to charging p-channel transistors that charge one plate of the capacitors. During half of the cycle, the charging p-channel transistor is off, allowing one plate of the capacitors (34,44) to discharge through an n-channel discharge transistor. After a period of discharge determined by the capacitance of the capacitor, the gate of a sub-threshold p-channel transistor (80) falls enough for sub-threshold current to flow, triggering the set or reset input of the S-R latch (40). Since sub-threshold currents are needed to toggle the S-R latch (40), the oscillator begins to oscillate below the threshold voltage.